In ancient Greek times Christians would be executed if they were found to be so. Therefore the ichthys (Jesus fish) was used as a way for two Christian to be made known to each other. In the ground, using a stick or staff, one man would draw the first arch of the ichthys and wait until another man would walk up and draw the second arch to finish it. This method would allow both men to know the other was a Christian without making the risk of voicing it.

Though back in those days they knew what the symbol actually meant, it was chosen by its simplicity. The ichthys is actually a symbol of fertility. In today's culture it is displayed on its side to look like a fish. Originally it was displayed with the football-shaped hole pointing upward and the open end downward. This showed what it truly represented, the vagina and anus of the fertility goddess Atargatis. Atargatis is also known in different cultures as Tirgata, Aphrodite, Pelagia or Delphine.

*looking at a car driving by with a jesus fish on the back*
"I see he's pro-vaginas."

A piece of fish-shaped plastic, usually made in China, designed to stick to the rear of mainly American owned vehicles to demonstrate to the rest of the world that the bearer prefers to ignore irrefutable evidence discovered by the most brilliant minds in science and base their smug, superior public personas on fairy tales and superstition, whilst engaging in closeted guilt-ridden sessions of drug-fuelled sexual deviance and other hypocrisy.